Escape or disallow ILPAddress reserved characters when creating accounts

[sappenin]

If an account has a disallowed character, we need to encode the value so that we don't accidentally add things into the ILP address during SPSP resolution. For example, if an account is created with an id of test+david (e.g., the + is an illegal character, the account will be created but the routing-table entry will be invalid (hermes will throw the following exception):

19:39:52.480 [qtp428061834-17] WARN  o.i.s.s.services.NewAccountService - Failed to create route
java.lang.IllegalArgumentException: The 'test+david' segment has an invalid format
	at org.interledger.core.InterledgerAddressPrefix$AbstractInterledgerAddressPrefix.check(InterledgerAddressPrefix.java:244)
	at org.interledger.core.InterledgerAddressPrefixBuilder$ImmutableInterledgerAddressPrefix.validate(InterledgerAddressPrefixBuilder.java:193)
	at org.interledger.core.InterledgerAddressPrefixBuilder$ImmutableInterledgerAddressPrefix.access$100(InterledgerAddressPrefixBuilder.java:117)
	at org.interledger.core.InterledgerAddressPrefixBuilder.build(InterledgerAddressPrefixBuilder.java:99)
	at org.interledger.core.InterledgerAddressPrefix.of(InterledgerAddressPrefix.java:70)
	at org.interledger.core.InterledgerAddressPrefix.with(InterledgerAddressPrefix.java:152)
	at org.interledger.spsp.server.services.NewAccountService.createAccount(NewAccountService.java:68)
	at org.interledger.spsp.s...

One thing that is not an issue is dots (.) (e.g., david.foo). These work properly.